Fuel cells have the great advantages that there is in a substantial sense no need for the fossil fuel which requires to pay attention to the depletion of resource, no or little noise is produced upon power generation, and the recovery of energy is high as compared with other energy power generation devices. The construction of fuel cells as relatively small size power generation plants installed in buildings and factories has been under development and some are used in practice. In particular, polymer electrolyte fuel cells operate at low temperature as compared with other types of fuel cell. They eliminate in a material aspect a concern about the corrosion of cell constituent parts and can discharge a relatively high current flow for low-temperature operation. They are thus of great interest not only as household cogeneration devices, but also as substitute power supplies for internal combustion engines on vehicles.
The polymer electrolyte fuel cells are constructed of several components including a separator which is generally in the form of a plate having a plurality of parallel channels in one or both surfaces thereof. The separator plays the roles of conducting to the exterior the electricity generated on the gas diffusing electrode within the fuel cell, discharging the water formed in the channels during the electricity generation process and maintaining the channels as a flowpath for reactant gas to flow into the fuel cell. Since the fuel-cell separators are required to be reduced in size, and a plurality of separators are used in stack, the sealing material generally takes the form of a relatively thin seal member having a thickness of less than about 2 mm. Therefore, there is a need for a separator sealing member which has improved strength and reduced compression set and remains fully durable in long-term service.
As the separator sealing member, sealing materials based on various resins have been under study in the art. Packing materials based on silicone rubber are often employed for their moldability, heat resistance and elasticity. The customarily used silicone rubbers are obtained by the curing of silicone rubber compositions of the addition curing type which are more effectively moldable. The customary silicone rubbers, however, suffer from the problem that compression set increases upon placing more importance on rubber strength whereas rubber strength becomes insufficient with more emphasis laid on compression set.